This invention relates to a cutting device for cutting optical fibers on the principle of stress rupture, and particularly a cutting device which can perform cutting of an optical fiber stably under predetermined conditions, thereby preventing the failure of the device and damage to the flaw forming blade or cut end face of the optical fiber due to excessive cutting.
As one method of cutting an optical fiber wire having a core made of glass, there is known a method that utilizes the principle of stress rupture. In this method, with tension applied to the optical fiber to be cut, an initial flaw is formed in the outer periphery of the wire by a flaw forming blade. Then, stress rupture occurs with the flaw as a starting point, so that the wire is cut at a right angle relative to its axis.
As devices for cutting an optical fiber wire on the principle of stress rupture, there are known ones disclosed in Japanese patent publication 4-123009 and U.S. Pat. Nos. 5108021 and 5460311, and one the applicant proposed in Japanese patent publication 2000-561409.
In conventional optical fiber cutting devices disclosed in these publications, if an optical fiber is properly and reliably set in a tension-imparting portion, the flaw forming blade cuts into the wire when the tension applied to the optical fiber reaches a predetermined value.
But in conventional devices, since the flaw forming blade is unconditionally linked to the motion of the tension-imparting portion, the relation between the moving amount of the tension-imparting portion and the magnitude of the tension applied to the optical fiber may vary due to unexpected situations such as poor clamp of the optical fiber, poor setting or trouble of portions or minor mistake of work. Thus, the flaw forming blade may cut into the wire at such a stage that a suitable tension is not applied to the optical fiber. In this case, even though the initial flaw is formed in the wire, stress rupture will not occur at this point of time, so that the blade is pressed against the wire with a stronger force.
If clamp of the optical fiber is insufficient, the flaw forming blade may abut the wire, which is moving by being pulled, and be abraded by the wire. In either cases, troubles in which the cutting edge of the flaw forming blade gets damaged or its cutting function is lost can occur.
Even if cutting is carried out normally under suitable conditions, in case the flaw forming blade does not stop but keep moving after cutting, the flaw forming blade may touch the cut end face of the wire, incurring damage or breakage of the end face.
In order to eliminate such trouble, it is required to reliably form an extremely shallow flaw in the outer periphery of a fine wire having an outer diameter of 0.1-0.3 mm when a suitable tension is applied to the wire, and also stop the flaw forming blade there. But with conventional cutting devices, in which the flaw forming blade is simply linked to the movement of the tension-imparting portion, it is difficult to meet such requirements.
With a method in which the movement of the flaw forming blade is stopped at a suitable position by providing a stopper, it is necessary to stop the blade immediately after a shallow flaw has been formed in the outer periphery of the wire. But since the setting position of the optical fiber delicately varies due to variations in the dimensions of fixed portions, there are cases in which the blade does not reach the wire and cannot form a flaw.
An object of this invention is to obviate these defects and disadvantages.
According to this invention, there is provided an optical fiber cutting device, comprising a tension imparting mechanism for imparting tension to an optical fiber to be cut, a flaw forming mechanism for forming an initial flaw for stress rupture in the optical fiber to which is applied the tension, the flaw forming mechanism comprising a blade table and a flaw forming blade mounted on the blade table for forming the initial flaw in the optical fiber, and a driving means for actuating the flaw forming mechanism, the flaw forming blade of the flaw forming mechanism being structured to move in proportion to the magnitude of the tension applied to the optical fiber.
This cutting device may be of a type that detects the tension applied to the optical fiber with a sensor and moves the flaw forming blade by means of an actuator by controlling the stroke of the actuator. But the following type is preferable.
In the preferable cutting device, the tension imparting means comprises a ferrule holding portion for holding a ferrule fitted on the optical fiber, a fiber-holding portion slidable in the longitudinal direction of the optical fiber for clamping a wire of the optical fiber protruding from the end face of the ferrule, a first resilient member for biasing the fiber-holding portion in a direction away from the ferrule-holding portion, and a lever coupled to the fiber-holding portion through the first resilient member so as to be movable relative to the fiber-holding portion, the driving means comprising a motion-converting mechanism for converting the relative movement between the fiber-holding portion and the lever to the motion of the blade table according to the amount of the relative movement to control the position of the blade table. Preferably this device may comprise a second resilient member for returning the lever so that the force of the second resilient member is transmitted to the fiber-holding portion through the lever, or the blade table and the blade of the flaw-forming mechanism are moved in the cutting direction by the force of a resilient member.
Since the cutting device of this invention carries out position control of the flaw forming blade according to the tension applied to the optical fiber, the flaw forming blade will not cut while a suitable tension is not applied or while the optical fiber is moving.
Also, since the tension is released when the optical fiber is cut, the movement of the flaw forming blade stops at this time, so that no excessive cutting will occur.
With the device according to the present invention, since relative movement occurs between the fiber-holding portion and the lever only when tension is applied to the optical fiber, and in association with the movement of the lever at that time, the blade table of the flaw-forming mechanism moves, the position of the flaw forming blade is automatically adjusted according to the tension applied to the optical fiber without using e.g. a tension-detecting sensor. Thus it is possible to achieve a simple, small and inexpensive device.
Also with this device, when the optical fiber is cut, the force stopping or holding the fiber-holding portion disappears and the fiber-holding portion is moved in such a direction as to decrease the amount of relative movement relative to the lever by the force of the first resilient member, so that the flaw forming blade is instantly returned from the cutting end point. Thus, it is possible to reliably eliminate the possibility of the end face of wire after cutting being abraded and damaged by the flaw forming blade.
Besides, the device in which a second resilient member for returning the lever or the one in which the blade table and the flaw forming blade are moved by the force of the resilient member is more simple and inexpensive and easier to operate.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: